about discriminating wisely between trend and noise, between low-frequency and high-frequency signals in time series of environmental variables (Air temperature in his example), apply as well to measurable quantities in ecosystems. Particularly relevant is the phenology of the species, which defines the timing of crucial recurrent events of their life cycle, like the date of first arrival to the nesting ground, the date of germination, the date of mating, the date of blooming etc. You may have noticed that I used examples related to birds and plants. Well, while phenology is a general concept, an empirical knowledge patiently accumulated by bird lovers and Sunday gardeners of the 19th and 20th centuries was first to be translated into systematic scientific surveys. And following rigorous statistical analyses of those long time series of observations, it has been firmly established that changes in the phenology of most species accompanied trends in temperature. The strength of the correlation is all the more important as the seasonality (latitude) of the ecosystem and the dependance of the species to their environment increase. The connection with climate change issues is straightforward. And it is not just about how one species or another will cope with changes of its environment, but rather about the interlocked interactions between all those species.
If you can easily think at a beautiful tulip as a species embedded in its environment, it is the same, in a more dynamic way, for planktonic marine species. Now oceanographers begin to benefit of the fruits of several long lasting monitoring programs. Unfortunately, the ever increasing pace of global climate change means that oceanographers are required to draw firm conclusions about the impact of environmental variability on ecosystems and develop predictive capabilities in the meantime ! And this will remain an elusive target as long as the mechanisms gearing those changes are not understood properly. Daunting task, as the changes in timing of such major event as diapause entrance and exit emerge form several layers of physiological and behavioral processes obeying their own dynamics while interacting with each others. But impossible is not known at the EML, so we decided to model the mechanisms behind the diapause of the dominant copepod Calanus finmarchicus
. We already know that even if it can produce several generation a year, this critically important species thrives in its seasonal environment (Northern half of the North Atlantic) thanks to its diapause strategy, which means killing time at depth in order not to be killed by the detrimental conditions prevailing at the surface in winter. For this purpose, it makes a feast on large phytoplankton cells (mainly diatoms) during the short period they are available, and build up impressive amount of energy rich lipid reserves. Those swimming droplets of lipid are in turn the basis for the rest of the upper trophic levels.
And what about changes then ? Things are more sparse there... Records of physiological properties related to the diapausing strategy are about a decade old now. Not enough really to study trends on climatological scales, but enough to understand that interannual variability is high (see figure). But abundance data are enough to see changes, especially in areas localized at its biogeographical fringe. In the North Sea for example, the ecosystem shifted from a copepod population dominated by 80% of C. finmarchicus
before the 60's to a present state dominated by 80% of its southern congener C. helgolandicus
. What is the role of diapause in that ? Not known yet. One thing is certain though: changes occur at an ever accelerating pace, and the unforeseen consequences for the ecosystems are likely to appear before our eyes while we are still racing to improve our understanding. I strongly wish that Copenhagen "talks" will end up with agreements as legally constraining on our leaders than the climate changes will be actually constraining on us.
Superimposed to the climatological (2004-2008) relative abundance of the different copepodid stages are box plots of the estimated dates of initiation (late winter) and termination (summer) of diapause in Calanus finmarchicus in the Gulf of Maine. Data from UNH COOC WB-7 station. Figure from James J. Pierson.